Semiconductor chips or wafers are used in many applications, including as processor chips for computers, and as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is usually necessary that during one or more phases of the manufacturing process, semiconductor devices must be polished, typically using chemical-mechanical polishing (CMP) techniques, to remove excess portions of materials that are deposited for various reasons during preceding manufacturing phases.
In linear CMP techniques, a polishing platen is closely spaced from a polishing pad or belt that is to polish the surface of the wafer sought to be polished, with a very thin air space, referred to as an "air bearing", being defined between the platen and the polishing pad. It is advantageous to maintain an air bearing between the platen and the pad to promote uniform polishing of the surface. More specifically, the polishing uniformity can be precisely controlled using an air bearing.
To maintain the air bearing, air source holes are formed in the platen and are arranged in concentric ring patterns from the center of the platen to the outer edge of the platen. Each ring establishes an air delivery zone. Air from an air source is directed through the holes during polishing, thus establishing the air bearing. Air is exhausted past the platen edge.
With multiple air delivery zones, it is desirable to radially vary the air distribution profile of the air bearing (to vary the polishing rate in each zone) as necessary to achieve optimal polishing. As recognized by the present invention, however, when air can be exhausted from all air delivery zones only past the platen edge, the distribution profiles of the zones are not completely independent of each other. This complicates establishing different distribution profiles for different zones. Fortunately, the present invention recognizes that is possible to establish greater independence of the air distribution profiles, zone to zone, to thereby facilitate establishing the polishing rate in each zone independently of the other zones and, hence, to improve manufacturing flexibility and functionality.